A VERSATILE SUN-LIT CONTROLLED-ENVIRONMENT FACILITY FOR STUDYING PLANT AND SOIL PROCESSES

A new environmental-tracking, sun-lit controlled-environment facility (terracosm) that can control and manipulate climatic and edaphic facto rs while maintaining natural environmental variability was developed t o study the effects of environmental stresses on a model ecosystem (i. e., plant and soil processes). An analysis of terracosm performance da ta indicates that the terracosms simulated natural seasonal and diurna l changes in atmospheric CO2, air and soil temperatures, vapor pressur e deficit (VPD), and soil moisture. The terracosm performance data ind icate that between 92 and 100% of the hourly CO2 concentrations are wi thin +/-50 mu mol mol(-1) of the target concentrations for both ambien t and elevated treatments (1 Nov. 1993 through 30 Nov. 1994). Air temp eratures are within 2 degrees C of the target temperature between 85 a nd 100% of the hours for both ambient and elevated temperature treatme nts. The VPD was approximately the same (0.09 kPa difference between t reatments) in the ambient and elevated temperature treatments. Distrib uted process control was implemented to minimize down-time. Terracosm downtime, periods when terracosm environmental conditions could not be reliably controlled, varied between 2.4 and 2.8% of all hours, and wa s equally distributed between biological sampling and equipment proble ms.